In the recent information-intensive society, there is an increasing demand for ensuring the security of information stored in a memory card or a memory chip (limiting an access to read) or preventing a third party from illegally rewriting or erasing data (limiting an access to write or erase).
As means for protecting stored information, there are known the method of storing a password in ROM of the memory card and permitting an access when the memory card is supplied with an input matching the password and the method of encrypting information to be stored, etc.